The subject matter disclosed herein relates to combined cycle power generation systems, and more specifically, to heat retention in their various components.
Combined cycle systems may generally include one or more gas turbines and steam turbines, which may be used to produce electricity in power plants. Within the gas turbine, fuel may be combusted to generate power. The heated exhaust gas discharged from a gas turbine may be sent to a heat recovery steam generation (HRSG) system as a source of energy, which may be used to produce steam for driving a steam turbine. Within the HRSG system, the heated exhaust gas may traverse a series of heat exchanger elements, such as superheaters, re-heaters, evaporators, economizers, and so forth. The heat exchanger elements may be used to transfer heat from the heated exhaust gas into condensate, which can then become superheated steam.
In general, the HRSG system may operate at a high temperature to produce the high temperature steam. During startup of the combined cycle system, auxiliary heat (outside the combined cycle flow, but within the power plant) may be provided from an auxiliary heating system to elevate the temperatures within the HRSG system to the desired high operating temperatures. When the gas turbine is operating, the exhaust gas may provide sufficient heat to maintain the high operating temperatures. However, the gas turbine may be shutdown at certain intervals, for example, during the night when the demand for electricity is low. During these gas turbine shutdown periods, components of the HRSG system, as well as other combined cycle components, may loose heat to the environment. After a shutdown period, additional heat may be input into the system to account for the heat lost to the environment and to return the HRSG system to the optimal operating temperature for producing high temperature steam. The input of additional heat may increase operating costs due to the use of the aforementioned auxiliary heating system.